You can use BigInteger class.
BigInteger bi1 = new BigInteger("637824629384623845238423545642384");
BigInteger bi2 = new BigInteger("3039768898793547264523745379249934");
BigInteger bigSum = bi1.add(bi2);
BigInteger bigProduct = bi1.multiply(bi2);
System.out.println("Sum : " + bigSum);
System.out.println("Product : " + bigProduct);
Output:
Sum : 3677593528178171109762168924892318
Product : 1938839471287900434078965247064711159607977007048190357000119602656
I should mention BigDecimal, which is excellent for amount calculations compare to double.
BigDecimal bd = new BigDecimal("123234545.4767");
BigDecimal displayVal = bd.setScale(2, RoundingMode.HALF_EVEN);
NumberFormat usdFormat = NumberFormat.getCurrencyInstance(Locale.US);
System.out.println(usdFormat.format(displayVal.doubleValue()));
Output:
$123,234,545.48